Studies are planned which will extend our knowledge about altered enzymes in old animals. Proof will be sought that in rats, these enzymes result from conformational rather than covalent changes. To this end, altered phosphoglycerate kinase (PGK) from old rat muscle will be unfolded in solutions of guanidine hydrochloride and allowed to refold. PGK from young rats will be treated similarly. If both forms of the enzyme were originally conformational isomers, the refolded products should be identical as demonstrated by spectral and kinetic properties. Such results were obtained with young and old enolase from the free-living nematode, Turbatrix aceti. In addition to its proved existence in old rat muscle, indications are that altered PGK exists in old brain and liver but not heart and kidney. Confirmation will be sought by purification of PGK from these sources. It will also be determined if altered enzymes exist in mitochondria of old rats. The turnover of PGK and soluble proteins in these tissues from young and old animals will be determined by use of a dual labeling technique. Thus, it can be seen if, as hypothesized, there is a relationship between changes in protein turnover and the alteration or non-alteration of an enzyme. The turnover data, in addition to its enzyme correlation, will have considerable intrinsic value. In T. aceti, protein turnover slows dramatically with age. Thus, the organisms should provide an outstanding model system for determining the factors responsible. Cell-free systems for protein synthesis from young and aging T. aceti will be compared for content and effectiveness of components such as initiation and elongation factors, aminoacyl-t-RNA synthetases and m-RNA. The same system will be utilized under conditions in which protein synthesis is reduced or cut off - e.g., hyponutrition or starvation. Thus, it should be possible to determine whether the regulatory mechanism (slowing) of protein synthesis is the same in aging as for other metabolic conditions. The results will be applied to studies in the aging rat. The findings will not only provide insight into regulation of protein synthesis in aging, but they will be applicable to other conditions, including disease, which affect protein synthesis.